1. Field of the Invention
This invention relates to a novel igniter assembly for igniting combustible compositions in a highly reliable manner, and in particular to an igniter assembly which includes a combustible illuminant composition and as actuated by deployment of an associated parachute. This invention also relates to devices comprising the novel igniter assembly, such devices including, by way of example, illuminating flares.
2. Description of the Related Art
Among the various environments in which illuminating flares are used, perhaps the most common environment for the use of flares involves the illumination of military battle grounds. In such applications, the flares are launched above ground or water areas suspected to contain enemy personnel and vehicles. Essentially, the illumination provided by the flare facilitates visual detection of the enemy personnel and vehicles, thereby providing more precise identification of target locations at which to aim arsenal. The illuminating effect provided by the flare is typically enhanced by equipping the flare with a parachute, which both increases the flight and time of descent for the illuminating flare and, upon deployment thereof, provides a requisite force for actuating an igniter housed in the flare.
The use of flares to ascertain the precise location of enemy targets can provide obvious military advantages. However, the availability and widespread use of military flares has negated this advantage somewhat, since there is an increased likelihood of opposing military forces also possessing flares. Thus, in order to gain a military advantage from the flares, it is paramount that the flares operate in a highly reliable and dependable manner, since flare failure can provide the opposing military force additional time to launch their own flares and arsenal.
An example of an illuminating flare that is reliable by conventional standards, e.g., about 87% of the time, is shown in FIGS. 5-7 herein. It is believed that one of the largest contributors, if not the largest contributor, to failed firing of this illuminating flare is the misfiring of the flare igniter. The flare, which is generally designated by reference numeral 200 in FIG. 5, comprises an aluminum casing 202 partitioned into two compartments. The forward compartment is the larger of the two compartments, and contains a solid illuminant fuel 204 designed to enhance nighttime vision and an igniter assembly 206 for initiating burning of the illuminant fuel 204. In the illustration, the aft compartment is the smaller of the two compartments, and contains a parachute 208 and a timing device (unnumbered). The timing device, inserted at an aft end of the casing 202, detaches from the flare casing 202 at a predetermined time to create a passageway through which the parachute 208 can deploy. Upon deployment through the passageway, the parachute 208 slows the rate of descent of the flare 200, thereby extending the time during which the burning illuminant fuel 204 is maintained at an elevated position. In this manner, the illuminating effect provided by the burning illuminant fuel 204 is enhanced.
A conventional igniter is disclosed in U.S. Pat. No. 4,155,306 and illustrated in FIGS. 6 and 7 herein. Referring to FIG. 6, the igniter 206 includes a housing 212 formed of a molded piece of LEXAN (polycarbonate) or light-weight metal. The housing 212 has longitudinally extending internal walls 213 and ridge 213a, which are receivable into an aluminum cap (not shown). The internal walls 213 and the ridge 213a define upper and lower hollow compartments 215, and a diametrically extending raceway 214 interposed between the upper and lower compartments 215. The raceway is defined in part by the ridge 213a of the internal wall 213. The ridge 213a has a depth less than that of the remainder of the internal walls 213. For convenience, the ridge 213a is shaded. The function of the ridge 213a is explained in further detail below.
A sliding cartridge (also referred to herein as a slider) 216 is disposed in the raceway 214 and is slidable along the raceway 214. The slider 216 comprises a spring-loaded striker arm 218, a torsion spring (located at position 220), and a pistol primer (containing small amount of explosive) 222. The striker arm 218 is depicted in a loaded or cocked position in FIG. 6. The torsion spring 220 urges the striker arm 218 to pivot about pin 224 and towards the position shown in FIG. 7, in which the striker arm 218 rests against the primer 222. A cam surface 225 of the housing 212 obstructs the striker arm 218 from moving towards the primer 222 and, in combination with the urging force of the spring 220, prior to actuation maintains the slider 216 in the position depicted in FIG. 6.
Located below the raceway 214 is a pellet cavity 226 containing an ignitable composition, such as boron potassium nitrate (BKNO3) pellets. The pellet cavity 226 is in communication with the solid illuminant fuel 204 through an orifice (not shown).
The slider 216 is operatively connected to the parachute 208 via cable or lanyard 230, which extends along a cable raceway (not shown) formed in the aluminum casing 202. The cable 230 contains a first swage ball 232 accommodated within recess 234 for securing the cable 230 to the slider 216. The recess 234 is in communication with a slot 236, which is sufficiently wide to permit passage of the cable 230, but to obstruct passage of the first swage ball 232. At the end of the cable 230 is a second swage ball (not shown, but positioned behind the first swage ball 232 in FIG. 6). The cable 230 extends between the first swage ball 232 and the second swage ball along an axial direction, that is, perpendicular to the portion of the cable 230 passing through the slot 236 (i.e., into the sheet on which FIGS. 6 and 7 are shown). The second swage ball is encapsulated into the internal wall 213. The encapsulation of the second swage ball in the internal wall 213 serves as a safety mechanism to protect against unintentional firing by preventing tension in the cable 230 from prematurely moving the slider 216 along the raceway 214.
In operation, the igniter assembly 206 is actuated by the force generated upon parachute 208 deployment. Upon actuation of the parachute 208, the deploying parachute pulls the cable 230 towards the aft end of the flare 200. When properly operated, the force imparted on the cable 230 by the deploying parachute 208 is sufficient to dislodge the second swage ball from the housing 212 and move the slider 216 in tandem with striker arm 218 and the primer 222 across the raceway 214 with sufficient force to overcome the frictional resistance between the cocked striker arm 218 and the cam surface 225, as well as the frictional resistance between the slider 216 and the raceway 214, thus passing the striker arm 218 under the cam surface 225.
After the slider 216 has moved a sufficient distance for the striker arm 218 to clear the cam surface 225, the urging force of the torsion spring 220 pivots the striker arm 218 about pin 224 and towards the primer 222, which is now located over the cavity 226 containing pellets. Impact of striker arm 218 against the primer 222 detonates the primer 222. The heat and flames generated by the detonation of the primer 222 pass through an orifice and ignite the BKNO3 pellets in cavity 226, which in turn ignites a wafer, which in turn ignites the solid illuminant fuel 204. Because the ridge 213a of the internal wall 213 extends in depth only a portion of the way across the depth of the raceway 214, a clearance is defined (between the ridge 213a and the opposing cap surface) through which the striker arm 218 can pass as the striker arm 218 pivots towards the primer 222.
Although effective by conventional standards, flares possessing the igniter assembly 206 function correctly only approximately 87% of the time. In the majority of the cases in which failure occurred, the slider mechanism 216 was found to have traveled only part of the way down the raceway, with the cable found either broken or intact. The reasons for these failures are believed to be as follows: The deployment of the parachute 208 imparts an instantaneous shock force to the cable 230, causing the second swage ball to dislodge from the slider wall in which the second swage ball is encapsulated. However, the remaining force imparted to the cable 230 by parachute deployment is not always sufficient to overcome additional frictional forces at the slider/raceway interface and the interface between the cocked striker arm 218 and the cam surface 225. These frictional forces can prevent the slider 216 from moving sufficient distance to clear the cam surface 225 and reaching and striking the primer 222. One reason for the high frictional force at the slider/raceway interface is that the cable does not pull at the center of the slider 216. Another reason is that the ridge 213a defining the top of the raceway 214 does not extend along the full depth of the slider 216 (in order to provide a clearance for passage of striker arm 218 as the striker arm 218 pivots from the cocked state to the firing state). The presence of this clearance is believed to allow the slider 216 to rotate somewhat about its longitudinal axis in the raceway 214 during sliding movement, thus increasing frictional forces.
It is, therefore, an object of this invention to overcome the above-discussed problems by the provision of an igniter assembly which reduces sticking of the slider in the raceway.
It is another object of this invention to provide an igniter assembly that has built-in safety features to significantly reduce the risk of the flare being accidentally fired due to impact. These safety features include, for example, the placement of the pellet cavity out of alignment with respect to the primer and striker arm prior to firing, and in one particularly advantageous embodiment, a static force minimum of preferably 50 lbs, more preferably 90 lbs, to cause ignition.
In accordance with a preferred embodiment of this invention, the striker arm and the primer are stationary relative to the igniter housing, in contrast to the known assembly shown in FIGS. 6 and 7. The pellet-containing chamber, which is stationary in the known assembly shown in FIGS. 6 and 7, is in accordance with the present invention incorporated into the slider so that the pellet chamber is not aligned with the striker arm in the cocked position. In the preferred embodiment, another feature for preventing the unintentional firing and ignition of the illumination composition involves providing the slider with a motion restricting bridge.
At least one of the following design features is desirably incorporated into the novel igniter assembly to accomplish the above and other objects, although the scope of the invention is not hereby limited. First, the igniter housing has raceway-defining walls having a depth (along the longitudinal direction of the flare) substantially equal to the depth of the slider, so that the slider does not contact any ridges during movement along the raceway. Second, greater symmetry is utilized in the slider to keep pulling forces in balance. Third, the distance of slider travel along the raceway is shortened. Fourth, the slider is made of a material that is more compatible with the igniter housing on a coefficient of friction basis. Fifth, the encapsulated swage ball is replaced by a less complex safety mechanism, such as a motion restricting bridge.
This invention is also directed to devices containing the novel igniter assembly. A representative non-limiting device intended to be covered by this invention is an illuminating flare.
This invention is also directed to a method of illuminating a field with an illuminating flare comprising the novel igniter assembly described herein.
Other objects, aspects and advantages of the invention will be apparent to those skilled in the art upon reading the specification and appended claims which, when read in conjunction with the accompanying drawings, explain the principles of this invention.